Yocaml.FilepathSourceAs Wordpress is mainly used to move files, having some functions to work with file names can be a very good idea!
Describing a filepath.
with_extension ext path returns true if path ends with ext false otherwise, ie: with_extension "html" "index.html" returns true but with_extenstion "html" "foohtml" returns false.
Add an extension to a t. For example: add_extension "index.txt" "html" will produce "index.txt.html".